On Aug. 11, a frantic husband called Darien police to report that his wife was missing.

A few hours later, a DuPage County sheriff's deputy found Dr. Xu "Sue" Wang's red Toyota parked on a gravel strip near the Waterfall Glen Forest Preserve. Her backpack, containing her credit cards, was locked inside.

Several days later, police found Wang's pager, beeping intermittently, on the side of a frontage road near Interstate Highway 55, a mile north of where her car was found.

In the seven weeks since, police and the FBI have found no more leads. Interviews with friends and colleagues of the 40-year-old physician were fruitless. Police also have not found any evidence--no weapon, no unknown fingerprint in the car, not even a ticket or travel receipt indicating that Wang may have decided to leave her life behind.

Now, after weeks of investigating the possibility that Wang chose to abandon her husband and young sons, detectives have concluded that Wang did not vanish willingly.

No one has been arrested or charged, but detectives have not ruled out Wang's husband, Yijun Zeng, as a suspect, saying they believe he is withholding information.

"We think (Zeng) is protecting himself, but from what, we don't know," said Deputy Police Chief Ron Campo, adding that Zeng has given misleading statements to investigators.

Zeng, himself a doctor who has stopped practicing because he suffers from Parkinson's disease, said he believes his wife was the victim of foul play but knows nothing about her disappearance.

"I swear, I did nothing to her," Zeng said. "Police checked out the house everywhere and found nothing."

In interviews with friends, police and Zeng, conflicting portraits of the couple emerge. Friends and associates of the couple said they appeared devoted to each other and their two sons, ages 9 and 6, and were active in the Chinese Christian Mandarin Church in Hinsdale.

But Campo said Wang's closest friends tell a different story: that the couple had been planning to divorce and had quarreled publicly as recently as a day before Wang disappeared.

Zeng and Wang met in Beijing when they were medical students and married in 1983. Six years later, they moved to the U.S. to work at the University of Pittsburgh Medical School.

In 1991, the couple moved to Chicago and worked at the University of Chicago Hospitals. Zeng did diabetes research until 1996, when his illness made it impossible for him to continue, he said. Wang worked in an obstetrics and gynecology lab until May 1998.

Then they went to Tulsa for Wang to begin her first-year residency, a requirement for her to practice medicine in the U.S.

In Tulsa, Wang worked with a Christian doctors group called In His Image. Although she was supposed to stay there for three years, she was unhappy with the program, Zeng and friends said.

Vicki Fink, a neighbor in Tulsa, described Wang as "a very sweet lady," dedicated to her patients and her sons.

"She loved those boys," said Fink, a nurse at the hospital where Wang was completing her residency. "She wouldn't leave them for anything."

Rev. Timothy Siswanto, pastor of the Tulsa Chinese Christian Church, said he counseled Zeng about the couple's marital problems, which he said were mostly related to the pressures of Wang's job and Zeng's desire to live in New York or another city where he had job prospects.

"They seemed like a good, close couple to us," Siswanto said. "I don't think that kind of argument is the main reason for her disappearance."

Zeng said he had received a consulting offer from a New York hospital and wanted to go there. But his wife insisted on returning to Chicago, where she began her second-year residency at Rush-Copley Medical Center in Aurora in June.

Police said the problems between Wang and Zeng may have come to a head in the days before she vanished. Friends cited two public arguments in particular.

Four days before Wang disappeared, police said, Wang called authorities in the Wisconsin Dells area after she couldn't find her husband. Zeng had been waiting in the parking lot of a water park while Wang took the couple's two sons inside. When Wang was ready to leave, her husband and the family car were gone.

Police found Zeng at a nearby casino, which infuriated Wang, said Hing Lo, a friend from Woodridge.

"The situation totally changed from her being nervous to angry," Lo said. "She wanted to know how he could leave his family alone to go to a casino."

Then, a day before Wang's disappearance, the couple had a loud argument in a cafeteria at Rush-Copley, police said.

Zeng said he and his wife disagreed on whether to spend money on swimming lessons for one of their sons.

"I didn't argue with her; she argued with me," Zeng said in a recent interview.

Campo said the substance of the spat was less troubling to investigators than Zeng's initial denial that the incident took place. When pressed, Campo said, Zeng acknowledged the couple quarreled at the hospital but said it occurred weeks before his wife disappeared.